This invention relates to differential pressure transducers and more particularly to diaphragm structures for differential pressure transducers to make possible the measurement of very low pressure differentials.
In energy management control systems such as those utilized to control the conditions in multi-story buildings, it is frequently necessary to make pressure difference measurements between indoor and outdoor air, between indoor and duct air, and between the air on various floors. All of these measurements are for the purpose of knowing where the air is moving, or trying to move. There may, for example, be openings which will allow air to move between floors of a multi-story building so as to cause much of the warm air to move to the upper floors. With proper measurement to detect this movement a computer may be used to calculate the action necessary from an associated control system to pump the air back to the lower floors. Other uses for pressure and pressure differential measurements include the measurement of air velocity in heating and cooling air ducts, where the pressure transducer is connected to a Pitot Tube.
The measurements mentioned above all involve transducers for measuring low pressure differentials (such as 1" to 10" of water, full scale). Such transducers must produce the standard 4-20 milliamp measurement signal and cost less than the typical low pressure units. The typical units generally have 4 or 5 inch diaphragms; and, because of those large diaphragms may be sensitive to the effects of gravity when in certain positions. Thus, the standard units for this service may sometimes give readings as high as full-scale when the differential is actually zero, if the transducer is positioned so that gravity can operate to deflect the diaphragm. In addition, the pressure housings associated with large diaphragms are expensive.
It is an object of the present invention to provide a small, light and, therefore, gravity insensitive and inexpensive diaphragm structure for pressure transducers, particularly of the capacitance type, for the measurement of low pressure differentials.